Oh I know what it does. I thought it would be a default setting that DJI would want always turned on. To discover its default is off made me question perhaps what some of the issues might be that you'd want to keep it off.

I have always made a habit of not relying on dji defaults as being the defaults I necessarily want. If you want the home point stored by your phantom to be the location of your device running the vision app, then enable it. If not then turn it off. Iv guess of you are moving a considerable distance from where the original home point is recorded you may want this turned on. Personally I have never used it. I would certainly test it some before I would trust it to do what it is advertised to do. I am sure there are many who use this. It is reliant on your device gps position so it is only as reliable as the accuracy of that. I will shut up now.

If your Display Device (iPhone, Ipad, Tablet, Android, etc) has a real time GPS you can set it on, but double check it because if non real GPS enabled Home Position won't be recorded dinamically and you could get into RTH if move away from initial take off point.
Here is shown a situation where DHPoint could have been best option:

If your Display Device (iPhone, Ipad, Tablet, Android, etc) has a real time GPS you can set it on, but double check it because if non real GPS enabled Home Position won't be recorded dinamically and you could get into RTH if move away from initial take off point.
Here is shown a situation where DHPoint could have been best option: